Fluid operated pumping device



Oct. 16, 1951 c. J. COBERLY FLUID OPERATED PUMPING DEVICE 2 SHEETS-SHEET 1' Filed March 25, 1946 Oct. 16, 1951 c. J. COBERLY FLUID OPERATED PUMPING DEVICE 2 SHEETS-SHEET 2 Filed March 23, 1946 17v vE/v TOIQ CLARENCE J Cass/24x,

Patented Oct. 16, 1951 UNITED STATES PATENT OFFICE FLUID OPERATED PUMPING DEVICE Clarence J. Coberly, Los Angeles, Calif., assignor, by mesne assignments, to Dresser Equipment 00., Cleveland, Ohio, a corporation of Ohio Application March 23, 1946, Serial No. 656,712

8 Claims. 1

My invention relates primarily to fluid operated pumps and, more particularly, to such a pump having a novel piston construction.

In the oil industry it is common practice to use a fluid operated pump in pumping oil from a well, such a pump generally comprising a coupled motor and pump combination set in the well at the level from which it is desired to pump the oil. In such a pumping device, the motor is normally actuated by admitting operating fluid, such as oil, under relatively high pressure alternately to opposite ends of a motor piston to reciprocate the same, the reciprocation of the motor piston being suitably communicated to a pump piston in the pump end of the device so as to pump oil from the well. In order to conduct operating fluid alternately to opposite ends of the motor piston, a suitable valve mechanism is employed. The valve mechanism may be similar to that disclosed in my Patent No. 2,134,174, issued October 25, 1938, although I prefer to employ my present invention in connection with a governing valve mechanism such as that disclosed in my Patent No. 2,311,157, issued February 16, 1943. However, it will be understood that my present invention may be employed in connection with any suitable valve mechanism other than those mentioned and, if desired, may also be employed in many installations independently of any such valve mechanism.

An object of my invention is to provide a shock absorbing or cushioning piston which may either be employed as the motor piston or as the pump piston of such a pumping structure to reduce the large accelerations frequently resulting from rapidly varying loads on the pumping structure. Ihe alternate application of pressure to the opposite ends of the motor piston, through a suitable valve mechanism produces controlled acceleration, at the beginning of each stroke, of the moving elements of the pump structure and the fluid column which is being lifted. The forces resulting from these accelerations at the ends of the stroke are ordinarily quite small as compared to the forces resulting from the high deceleration of the moving system and the operation fluid column and acceleration of the pumped fluid column which may occur at some intermediate point in the stroke if the fluid being pumped contains free gas.

In pumping oil from a well. the well oil f equently contains mixed therewith or in solution therein varying quantities of natural gas produced from the well together with the oil. the quantity of such gas depending upon the amount of gas in the producing formation with the oil and the bottom hole conditions of temperature, pressure, mechanical agitation, etc. Furthermore, it is common experience in the oil industry that the quantity of gas in the oil entering the pump in a particular well frequently varies within wide limits at different times during production from the well. Since displacement type pumps are most commonly used to pump oil, considerable difficulty has been experienced, with gas being released within the pumpcylinder due to agitation and pressure drop through the intake valves and passages, thus reducing materially the pumping load until the pump piston compresses this gas and strikes solid well fluid in the pump cylinder. Similar pumping load decreases may result from operating the pump with the pump intake valve plugged, or from operating the pump beyond the fluid capacity of thewell so that gas is present in the pump cylinder.

In fluid operated pumps, if the pumping load on the pump piston decreases for any of the reasons mentioned above, or for any other reason,

the entire pumping mechanism tends to accelerate very rapidly until the pump piston strikes solid well fluid in the pump cylinder.

This acceleration may continue until the piston velocity greatly exceeds that corresponding to the rate of supply of the operating fluid. This results from the fact that this operating fluid has an appreciable compressibility at the required operating pressure and the volume of operating fluid contained in the power oil tubing is large. When the pump load decreases for any reason the operating fluid ex ands driving the piston ahead at a high speed limited only by the friction losses in the tubin and fluid passages in the engine.

T0 visuali e the amount of this expansion assume an 8. 00 ft. well with an operatin pressure 3.000 pounds per square inch. At this pressure the power fl id is compressed 1.5%, or 12 feet expressed as len th of fluid column. The area of the inside diameter of the power tubing is approximately canal to that of the en ine iston so the en ine iston wou d t avel 19.0 feet hefore the ower fluid in the system would be expanded to 0 pounds per square inch. The stroke of the piston may be 2 feetso that at the end of the first stroke the pressure would be reduced to only 250 pounds per souare inch. Therefore. during the first stroke the average pressure which would have to be consumed in friction wo ld be 2950 pounds per souare inch. The resultin velocity to develo this friction loss might drive the piston When the pump station piston hits the well fluid, the entire pumping mechanism decelerates substantially instantaneously to almost zero speed and then accelerates again until the well fluid in the tubing is brought up to normal speed. Such negative accelerations or decelerations may be of extremely large magnitude and introduce hydraulic shock loads'which result in abnormal stressingof the parts of the pumping mechanism and which may cause considerable damage in the form of excessive wear, scoring, seizing, or even breakage of the parts. By-employing .my shock absorbing piston as either the motor piston or the pump piston, the magnitudes-of such decelerations are greatly reduced to minimize hydraulic shock loads on the pumping-structure by distributing the deceleration and .acceleration of well fluid over longer periods of time, thus providing for more uniform operation of the pumping mechanism.

A' fur-ther object of the zinvention s to provide in such a fluid operated pump a piston which is loosely connected to its piston rods so that :the piston will be self-:aligningrbetween the rods and 'thebore of the cylinder .in which itreciprocates. "This feature eliminates the necessity of working 'to close tolerances in maintaining accurate concentricities of the :parts.

Other objects and advantages will appear from the following specification and the drawings, which are for the purpose of illustration only, and in which:

Fig. 1 is a vertical sectional view showing a fluid operated pump including my invention 'as installed in a well;

Fig. 2 is an enlarged vertical sectional view showing the motor section of the pump illustrated in Fig. 1;

Fig. 3 is a vertical sectional View showing the pump section of the invention and is a downward extension of Fig. :2;

Fig. '4 is a vertical sectional view showing the lower end of the pump and is a downward extension of Fig. 3;

Fig. 5 is a further enlarged vertical sectional view of the motor piston assembly shown in Fig. 6 is a graph illustrating the operation of the invention.

Referring particularly to Fig. "1, I show a, well casing H which extends downwardly from a casing head 12 into the oil producing formation of a 'well, the lower end of "the casing being provided'with conventional perforations I la. From a fitting i3 forming an intermediate part of the casing head i2, a production tubing 14 extends downwardly through the casing I i into a "body of oil 15 in the lower portion thereof. The "lower end of the production tubing It is equipped "with a pump seat'lfi adaptedto receive and support the lower inlet end 11 of a fluid operated "pump 18. A power tubing 19 extends downwardly through the production tubing 14 and has its upper end connected to a cap member 20 of the casing head 12, the lower end of the tubing 19 being connected to the pump I8.

The pump 18 comprises a. lower pump section 2! and an upper motor section 22, best shown in Fig. 2, including a motor cylinder 23, the lower end of which is connected -to a pump cylinder 25, best shown in Fig. 3. The motor cylinder 23 is provided with a cylinder liner 21 therein,

there being longitudinal passages 28 therebetween, the liner having a bore 29 in which is provided a reeiprocable motor piston'assembly 30.

The motor section 22 is provided near its lower end with ports 32 which communicate between the passages 28 and the bore 28 adjacent the lower end of the bore. The upper end of the bore 2? communicates through ports 33 with a passage Bt. The passages 28 and 34 extend upwardly to a valve mechanism (not shown) which is adapted to introduce operating fluid from the power tubing 19 alternately in'to the passages 28 and 3t and thus alternately into the bore 29 at opposite ends of the motor piston 30 to reciprocatethe-piston-the motor piston being connected to the valve mechanism by an upper pilot rod 35. As previously mentioned, the valve mechanism may be of any suitable construction such as that disclosed in my aforesaid Patent No. .2,13 i,l74.,although I prefer to employ the governing valve mechanism disclosed in my aforesaid Patent'No. 2,311,157.

As best shown in Fig. 3, the pumping cylinder 2511s provided with .a tubula-a'oylinder dimer 31 therein providing longitudinal passages 38 therebetween, the liner :having a bore :39 in which is disposed a Lrecipro'cable pump piston 49. .The motor :piston 33 and pump :piston All are i601!- nect'ed by anintermediatepiston rod-"42 by which reciprocation of the .motor piston is :communi- .cated 'toithe pumppiston. ltwillbeinoted that the pilot rod I35, the motor piston -.39, the :inter- :mediate piston rod #2, .and the pump piston 40 are all provided with .axial passages 53 which connect with an axial passage Minn. flower piston'rod t5, the lower piston rod-being connected to the lower end-oi the'pumptpiston andextend- -downwardly therefrom. Theipurpose of .th'e

passages flfiand t l is 'to provide flui'dcommunication through the rods 35,132and 45 to balance the fluid pressure ton itherupper and lower ends of "the rods 'as more fully described :in'niy said Patent No. 2,311,157.

The general operation of the fluid operated pump Sis well known in the art,'-bein described in detail in my aforesaid Pamnt No. 2,134,174, and needs be described only briefly herein. Op-

crating fluid, 'such as, for example, clean oil,

is supplied under relatively high pressure to the casing head 12 through a supply tubing -48 'con :nected thereto and leading from a suitable source of operating fluid (not shown) andflows downwardly through the operating fluid tubing #9 to the pump 18 to actuate .thesa-me. Such operating fluid is alternatively supplied to opposite ends of the motor piston 39 through the passages .28 and 34 to reciprocate the motor piston. Re-

; ciprocation of the motor piston 3t operates through the intermediate :piston rod 42 to similarl reciprocate the pump piston 59, which is .of the double-acting type and draws oil from the reservoir 15 through the pump inlet into the liner 3'! of the pump cylinder .25 andexpels 'it therefrom into the production tubing 14 through discharge ports 48. Such pumped oil flows upwardly through the production tubing 14 and through the casing head i2, being discharged therefrom into a discharge tubing d9 through which it is conveyed to a point 'of use.

or storage (not shown).

As previously indicated, my -shock absorbing piston may be employed as either the motor piston 30 or pump piston 40 of the pump t8, although it will, of course, be understood that I do not intend to be limited'to the particular pumping mechanism described heretofore, since the shock absorbing piston may be employed in connection with other suitable pumping structures or may be employed in installations other than pumping installations if desired.

The motor piston 30, including features of the invention, is best shown in detail in Fig.5, and

includes an outer tubular piston sleeve 50 provided with annular grooves 5| in which conventional piston rings 52 are retained, the piston rings forming a sliding fluid tight fit with the bore 29 of the motor cylinder liner 21. The ends of the pistonsleeve 50 are substantially closed by an upper head 53 and a lower head 54, the heads being suitably threaded intothe sleeve, to form a central chamber 55. The upper head 53 is provided with an axial bore, 55'through which the pilot rod 35 extends, and the lower head 54 is provided with an axial bore 5'! through which the intermediate piston rod 42 extends. The rods 35 and 42 preferably have the same external diameter, and the bores 56 and 5'! are sufilciently larger than this diameter to'provide clearances 58 and 59, respectively, therebetween, these clearances preferably being in the order of .002 inch or more per inch of diameter of the bores.

Provided in the central chamber 55 is a cylindrical plunger 6| into which the lower end of the pilot rod 35 and the upper end of the intermediate piston rod 42 are suitably threaded, the plunger being of slightly less external diameter than the internal diameter of the central chamber to form a clearance 62 therebetween which is preferably of the same order of magnitude as the clearances 58 and 59. The plunger 6| has an upper end 63 and a lower end 54 and is substantially shorter than the chamber 55, so that when the upper end engages the upper head 53 the lower end will be spaced from the lower head 54, and vice versa. Due ,to the clearances 58, 59, and 62, the concentricities of the parts of the motor piston 30' do not have to be accurately maintained to provide a free sliding fit in the bore 29, as the parts of the piston may adjust themselves radially, within limits, to compensate for any minor inaccuracies in fabrication.

Assuming that the motor piston 39 and the pump piston 49 are at the upper end of their strokes, as shown in Figs. 2 and 3, pressure is applied to the upper end of the motor piston by the operating fluid to drive the motor piston downwardly. Assuming that gas is present in the liner 3'! of the pump cylinder below the pump piston 40, the motor piston will tend to drive the pump piston downwardly very rapidly at a high initial speed, as represented by the portion 19 of the curve shown in Fig. 6, until such gas is compressed and the pump piston strikes solid, or relatively incompressible, fluid, represented by the peak 1 I of the curve of Fig. 6. If a conventional piston were used as the motor piston 30, upon the pump piston striking solid fluid both pistons would decelerate substantially instantaneously to produce a deceleration peak of large magnitude and short duration, such as that illustrated by the portion I2 of the curve of Fig. 6, so that the speed of the moving parts of the pumping'mechanism would be reduced very quickly from the high initial speed thereof to nearly zero and then increase to a normal operating speed commensurate with the volume. of operating fluid supplied to the motor cylinder through ports 33 and 34 and applying pressure to the motor piston 30. Such a rapid deceleration of the motor and pump pistons 30 and 40 may introduce hydraulic shock nism. It will be apparent that such large accelerations and de'celerations -of the moving parts of the pumpin mechanism l-8 may occurwhenoperating the pump beyond the capacity of the well, by operating the pump with inoperative pump valves, or under various other conditions, as well as by operating the pump with oil which contains gas.

Since operating fluid under relatively high pressure is alternately admitted to the opposite ends or the motor piston 30, such fluid will flll the clearances 58, 59, and 62 and the central chamber around the plunger 6|, to provide a fluid cushion'between the plunger and the heads 53 and 54. As the plunger 6| may move' longitudinally. relative to the heads 53 and 54, and as the-plunger is shorter than the central chamber 55, a lower space 6'! may be formed between the lower end 64 of the plunger and the lower head 54, and an upper space 68 may .be formed between the upper end 63 of the plunger and the upper head 53 when the plunger is in its lowermost position with its lower end 64 in engagement with the lower head as illustrated.

As illustrated in Fig. 5, the motor piston 30 has just completed an upstroke and is ready to commence its downstroke, and the pump cylinder liner 31 below the pump piston 40 is filled with solid well fluid. Upon the admission of operating fluidunder pressure to the upperface 69 of the motor piston 3|], such pressure will exert a downward force on the upper head 53 to loads of suflicient intensity to cause considerable damage to the components of the mechamove it downwardly. The piston rod 42 and plunger 6| will tend to remain stationary, and, consequently, the downward movement of the upper head will build up a fluid pressure in the upper space 68, and will tend to reduce the fluid pressure in the lower space 61. If the liner 3! of the pump cylinder is full of solid fluid below the pump piston 40, such pressure in the upper space 68 will build up immediately to a relatively high value, and as soon as the pressure in the upper space 68 rises above the pressure in the lower space 61 it will cause a flow of fluid from the upper space through the clearance 58 to the upper end of the piston where the pressure is being applied. Fluid will also flow from the upperspace 58 through the clearance 62 to the lower space 67. Also, since fluid pressure in the lower space 61 will be lower than the fluid pressure in the motor cylinder below the motor piston 30, fluid will also flow into the lower space 61 from this source. The intermediate piston rod 42 will be held against movement by the pump load exerted on the pump piston 40, and hence the plunger 6| will exert a force opposing the pressure applied to the upper face 69' of the motor piston.

The product of the fluid pressure difference between the spaces 61 and 68 multiplied by the difference between the cross-sectional area of the plunger BI and the cross-sectional area of the intermediate piston rod 42 must exceed the upward force exerted by the piston rod 42 before that rod will move downwardly. The difference in pressure between the spaces- 6'! and 68 will depend upon the rate at which fluid pressure is applied to the upper face 69 of the motor piston and to the clearances 58, 59, and 62 between the parts, and upon the viscosity of the operating fluid. Therefore, since such clearances can be readily controlled in manuiacture, with a given operating fluid the accelscam-pee a "eration of the piston rod 42 and the pump ;pis'- "-ton4fl c'anbe readily controlled.

Leakage of operating fluid through the clear- :ances58, 59, and 52 will continueas the upper head 53 moves downwardly relative to the plunger Bl until the upper end'B3 of the vplunger engages the uppefl head 53, at which time such relative movement stops and the total force of "the fluid pressure applied to the upper face 69 will be exerted downwardly on the plunger and hence on the pump piston 40 through the interniedlat'e piston rod 42. Thus, 'the pump piston "'40 will accelerate until it is. travelling on its 'dow'nstrok'e at the normal pumping speed. Due to the lost motion between the'upper head '53 and the plunger Bl, however, the full pump load is applied relativelyslow'ly "to the motor piston, thus preventing 'fiuid shock on the com- --mencement of the downstroke of thepistons.

ln the "event that the motor piston starts its downward travel as i'lescimibed above when there is gas in the'liner 3i of the pump-cylinder 25 below the pump piston 453, the motorpiston assembly, consisting of theisleeve 58, :heads 53 and 54, and the plunger 6l, will move downwardly as a unit because very little downward force is "required tomove the motor piston when no substantial load "is on the pump, and hence very little fluid pressure differential will be created between the spaces 'G'l' and Gdand the rate of leakage therebetween will "be small. Therefore, very little if any relative movement between the upper head 5'3 :and the plunger ill will takeplace during movement of the motor piston under such a condition of substantially no load. If the liner 3''! of the pump cylinder'-25"is entlrelyfilled with gas *below the pump piston, the motor ipiston Bil and the pump piston will thus move downwardly together at a rate higher than normal throughout their --strokes. the liner 3'! below the pump :piston 43, both pistons will still =move downwardly together until such gas is compressed and the pump piston strikes the solid fluid, represented by the peak H on the curve of Fig. '6, at which 'time'pre'ssure "will build up in the upper space 68 and-decrease in the lower space 6 and the lost motion will be taken up by the flow of operating fluid through the clearances 51, 58 and 62,as described above, permitting a deceleration'of a relatively low magnitude, as illustrated by the portion T3 of the If there is some solid'fiuid in curve of Fig. '6, thus gradually absorbing the increase in pump load and reducing hydraulic shock efiects, which are undesirable, as pointed out above. As "will be apparent, on the upstroke 'of the motorpiston 3B and pump piston 40, the

relative movement-of the parts -is merely reversed.

From the foregoing it will be understood that by virtue of my invention the cushioning action of the motor piston 30 is substantially the same when the pump piston Ml strikes solid fluid after travelling a substantial distance with no appreciable load as it is upon normal starting when the pump cylinder 25 is filled with solid fluid. Thus, I can provide an effective cushion against hydraulic shock effects occurring at any point in the stroke of the pump piston 40, that point being where full load is applied and where hydraulic shock would otherwise occur.

Although I have disclosed an exemplary embodiment and an illustrative application of my invention, I do not intend to be limited to the specific disclosures contained herein, since my invention is susceptible to other applications and since various changes, modifications, and substi- 8 tutions may be incorporated in the embodiment disclosed without'departin'g from the spirit of the invention. Consequently, I desire to be afiorded the protection offered by the full scope of my appended claims.

I claim as my invention:

1. In a fiuid operated pump, the combination of a motor cylinder; a motor piston in said motor cylinder; a pump cylinder; a pump piston in said pump cylinder, one of said pistons having a movable sleeve element having a chamber therein and having a movable plunger element in said chamber and movable relative to said sleeve element, said plunger element being shorter than said chamber to provide a space therebetween at both ends, said plunger element being of smaller diameter than said chamber so as to provide an annular clearance therebetween connecting said spaces; and piston rod means connecting said plunger element and the other of said pistons.

2. In 'a fluid operated pump, the combination of a motor cylinder; a motor piston in said motor cylinder; a pump cylinder; a pump piston in said pump cylinder, one of said pistons having amovable sleeve element having a chamber therein and having a movable plunger element in said chamber and movable relative 'to said sleeve element, said plunger element being shorter than said chamber to provide a space therebetween at both ends, said plunger element 'being of smaller diameter than said chamber so "as to provide an annular clearance therebetween connecting said spaces, said clearance being approximately 0.002 inch per inch of diameter of said chamber; and piston rod means connecting said plunger element and the other of said pistons.

3. In a fluid operated pump, the combination of: a motor cylinder and a pump cylinder; a pump piston in said pump cylinder; a piston rod connected to said pump piston and extending into said motor cylinder; and a motor piston in said motor cylinder, said motor piston including a sleeve element adapted to provide a close sliding fit with the wall of said motor cylinder, said sleeve element enclosing the end of said piston rod and providing an annular chamber therearound, a plunger disposed in'said chamber and rigidly connected at one of its ends to said'piston rod, said plunger having a length less than that of said chamber and having an external diameter less than the internal diameter of said chamber so as to provide a first annular clearance therebetween, a pilot rod rigidly connected to the other end of said plunger and extending from said sleeve element, and means substantially closing the ends of said chamber and encircling said rods so as to provide second annular clearances between said means and each of said rods, each of said second annular clearances communicating with said chamber.

4. In a fluid operated pump, the combination of: a motor cylinder and a pump cylinder; a motor piston in said motor cylinder; a piston rod connected to said motor piston and extending into said pump cylinder; and a pump piston in said pump cylinder, said pump piston including a sleeve element adapted to provide a close sliding fit with the wall of said pump cylinder, said sleeve element enclosing the end of said piston rod and providing an annular chamber therearound, a plunger disposed in said chamber and rigidly connected at one of its ends to said piston rod, said plunger having a length less than that of said chamber and having an external diameter less than the internal diameter of said chamber so as to provide a first annular clearance therebetween, a pilot rod rigidly connected to the other end of said plunger and extending from said sleeve element, and means substantially closing the ends of said chamber and encircling said rods so as to provide second annular clearances between said means and each of said rods, each of said second annular clearances communicating with said chamber.

5. In a fluid operated pump, the combination of: a motor cylinder; a motor piston in said motor cylinder; a pump cylinder; a pum piston in said pump cylinder, one of said pistons being hollow to provide a chamber therein and having a plunger element in said chamber and movable relative to said one piston, said plunger element being shorter than said chamber, said plunger element being of smaller diameter than said chamber so as to provide an annular clearance therebetween throughout the length of said plunger element; and piston rod means connecting said plunger element and the other of said pistons.

6. In a piston means for a fluid operated pump, the combination of: sleeve means adapted to form a fluid-tight sliding fit with the interior of a cylinder; head means rigidly secured to one end of said sleeve means to provide a cylindrical chamber in said piston means; plunger means in said chamber, said plunger means being smaller in diameter than said chamber so as'to provide a clearance forming a fluid passage therebetween, said plunger being substantially shorter than said chamber; and rod means extending through said head means into said chamber and connected to said plunger means, said head means having a bore through which said rod means extends, said bore being of greater diameter than said rod means so as to provide a clearance forming a fluid passage therebetween.

7. In a piston means for a fluid operated pump, the combination of: sleeve means adapted to form a fluid-tight sliding fit with the interior of a cylinder; first head means rigidly secured to' one end of said sleeve means to provide a cylindrical chamber in said piston means; second head means secured to the other end of said sleeve means; plunger means in said chamber, said plunger means being smaller in diameter than said chamber so as to provide a clearance forming a fluid passage therebetween, said plunger being s bs a tially sh t r t an a cham e firs rod means extending through said first head means into said chamber and connected to said plunger means; and second rod means extending through said second head means into said chamber and connected to said plunger means, said head means each having a bore through which said rod means extends, said bore being of greater diameter than said rod means so as to provide a clearance forming a fluid passage therebetween.

8. In a piston means for a fluid operated pump, the combination of: sleeve means adapted to form a fluid-tight sliding fit with the interior of a cylinder; first head means rigidly secured to one end of said sleeve means to provide a cylindrical chamber in said piston means; second head means secured to the other end of said sleeve means; plunger means in said chamber, said plunger means being smaller in diameter than said chamber so as to provide a clearance forming a fluid passage therebetween, said plunger being substantially shorter than said chamber; first rod means extending through said first head means into said chamber and connected to said plunger means; and second rod means extending through said second head means into said chamber and connected to said plunger means, said head means each having a bore through which said rod means extends, said bore being of greater diameter than said rod means so as to provide a clearance forming a fluid passage therebetween, said rod means and said plunger means being tubular in form to provide a continuous fluid passage therethrough.

CLARENCE J. COBERLY.

REFERENCES CITED The following references are of record in the" file of this patent:

UNITED STATES PATENTS Number Name Date 92,957 Gould July 27, 1869 456,016 Canet July 14, 1891 850,583 Howard Apr. 16, 1902 1,160,976 Myers Nov. 16, 1915 1,592,912 Thompson July 20, 1926 1,956,988 Lapointe May 1, 1934 2,081,220 Coberly May 25, 1937 2,087,426 Becherean et al. July 20, 1937 2,134,174 Coberly Oct. 25, 1938 2,311,157 Coberly Feb. 16, 1943 2,312,857 Woelfer Mar. 2, 1943 

